I have a hot water heater in my boat that is being held together by rust. I haven't got it out of the boat yet, but it doesn't look like a fun job. The previous owner gave me a brand new one with the boat that is a small (2 gal) household unit (120V). My question is, should I use this unit or should I buy one that heats from running the engine and 120V?We will mostly be in a slip with shorepower when using, and don't motor for long periods of time. we sail!Thanks,Dave